Cryogenic turbo-molecular vacuum pump



Oct. 27, 1970 o. P. BREAUX 3,536,418

CRYOGENIC TURBO-MOLECULAR VACUUM PUMP Filed Feb. 13, 1969 2 sheets-sheet1 70 j 477Mo SPWM( lol/NP cfm/v e Le ra A @f INVENTOR.

0162/06 l. l 0x BY n/y 0t- 27, 1970 o. P. BREAUX 3,536,418

CRYOGENIC TURBO-MOLECULAR VACUUM PUMP Filed Feb. 15, 1969`2.snetS14-she@t z g; frz/e Paw/P u Q mw# sw U M5 u u.

IN VEN TOR. a/vz /nf 0. Mtnl WJM" 3,536,418 Patented Oct. 27, 19703,536,418 CRYOGENIC TURBO-MOLECULAR VACUUM PUMP Onezime I. Breaux, 104E. 3rd St., Dayton, Ohio 45402 Filed Feb. 13, 1969, Ser. No. 799,003Int. Cl. F04b 19/16, 19/22; F17c 7/02 U.S. Cl. 417-49 7 Claims ABSTRACTOF THE DISCLOSURE A turbo-molecular pump is cooled to cryogenicternperature with liquid helium so that the particles being pumped havevery low thermal energy. The outlet pressure of the turbo-molecular pumpis reduced to about l-12 torr so that the reduced outlet pressure incombination with the low thermal energy of the particles substantiallyeliminates backstreaming through the turbomolecular pump thus providingmuch higher vacuum in the chamber to be evacuated.

BACKGROUND OF THE INVENTION This invention relates to vacuum pumps forobtaining ultrahigh vacuum.

In simulating outer space conditions there is a continuing effort toobtain ultrahigh vacuum. Prior art systems which are used to obtainultrahigh vacuum are the cryogenic vacuum pump, which is based on thecondensation of gases and vapors on metal surfaces which have beencooled by substances at a very low temperature, such as, liquid helium,and the molecular pump wherein the molecules strike a moving surfacewhich gives the molecules a resultant velocity in the direction ofmotion of the surface. Channels cut in a stator adjacent the movingsurface direct the movement of the molecules such that a pumping actionis produced. Cryogenio pumps will not effectively pump neon, helium orhydrogen, and molecular pumps suffer from backstreaming. Since thesegases are always present in air, a vacuum of about -12 torr has been thelimit of prior art pumping systems.

SUMMARY OF THE INVENTION According to this invention, a vacuum pump isprovided which gives improved results in obtaining very high vacuums. Inthe device of the invention, a conventional turbo-molecular pump iscooled with liquid helium. The outlet pressure on the pump is reduced toabout 10-12 torr, or lower, by conventional pumping. By reducing theoutlet pressure and by cooling theturbo-molecular pump, such that theparticles have very low thermal energy, backstreaming through themolecular pump is substantially eliminated. This backstreaming throughthe molecular pump will be reduced even when neon, helium, and hydrogenare the materials being pumped. Thus the device of the invention may beused to obtain higher vacuum than prior art devices.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a partially schematic blockdiagram of a high vacuum pumping system according to the invention; and

FIG. 2 is a partially schematic block diagram of another embodiment ofthe device of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIG. l of thedrawing, reference character 10 shows a conventional turbo-molecularpump with a rotor 11 having a shaft 12 and a plurality of radial blades13 and a stator 15 having a plurality of blades 16 interleaved betweenblades 13. Such a pump can be found on page 200 of High Vacuum PumpingEquipment, by Powers, Reinhold Publishing Corporation, New York, 1966.

The pump 10 is located within a chamber 17 which is hermetically sealedexcept at the inlet and outlet and has its rotor 11 supported byconventional magnetic bearing 18 and 19. The magnetic bearings reducingthe frictional heat added to the system. The rotor 11 is driven by a`conventional induction motor shown schematically at 20. The rotor 21and the stator 22 of motor 20 are located within the jacket 23 to reducethe heating effect of the motor by reducing the resistance in the motorwindings. Leads L for the stator 22 are brought out through a liquidseal S. The fluid-tight jacket 23 is positioned around chamber 17 andhas liquid helium supplied to it from supply 24. A valve 25 controls theflow of helium to jacket 23. The inlet end 26 of pump 10 is connected tothe chamber 27 to be evacuated. The outlet ends 28 of pump 10 areconnected to a cryo pump 29, a diffusion pump 31 and a roughing pump 33.Valves 34, 35, and 36 are provided to bypass the diffusion pump duringinitial pump down. Cryogenic pumps can be found in chapter 7 of the textHigh Vacuum Pumping Equipment reference above. The diffusion pump isdescribed in chapter 2 of the same text. A Roots pump described inchapter 5 or an oil seal pump described in chapter 1 of the same textmay be used for the roughing pump.

In the operation of the device, valves 34 and 35 are closed and valve 36is opened and roughing pump 33 is started to bring the system toapproximately 10H3 to 10-5 torr. The pump 10 is then started, the cryopump 29 is supplied with coolant, valves 34 and 35 are opened and valve36 is closed. The diffusion pump 31 is then started and the system ispumped to provide a pressure of about 10-12 torr at the outlet of theturbo-molecular pump. The `cryogenic pump 29 reduces backstreaming fromthe diffusion pump 31. Valve 25 is then opened to admit liquid helium tothe jacket 23. With the outlet pressure at the outlets 28 of pump 10, at10-12 torr, and with the cooling effect of the liquid helium on theturbo-molecular pump, much higher vacuums are attainable in chamber 27.

While one system is shown in FIG. l for attaining a vacuum of 10-12 torrat the outlets 28- of pump 10, other systems may be used, for example,as shown in FIG. 2, a Getter Ion Pump 37, as described in chapter 9 ofHigh Vacuum Pumping Equipment, may be used together with cryogenic pump29.

The parts within the pumping system are preferably made of stainlesssteel or other material which will not outgas and contaminate thesystem. Those parts that cannot be made of stainless steel such as themagnetic bearing, can be covered with stainless steel.

There has thus been provided a vacuum pumping system for obtaininghigher vacuum than prior art systems.

I claim:

1. A system for providing very high vacuum in a chamber to be evacuated,comprising: a turbo-molecular pump having an inlet and an outlet: saidturbomolecular pump being located within a housing which is hermeticallysealed except for said inlet and said outlet; said inlet being connectedto said chamber to be evacuated; means for reducing the pressure at theoutlet of said turbo-molecular pump to at least 10-12 torr and means forcooling said turbo-molecular pump to approximately the temperature ofliquid helium.

2. The device as recited in claim 1 wherein said means for reducing thepressure at the outlet of said turbomolecular pump includes a roughingpump for initial pump down, a diffusion pump for further reducing thepressure to approximately 10-12 torr and a cryogenic pump to impedebackflow from the diffusion pump.

3. The device as recited in claim 2 wherein said turbomolecular purnpVhas a rotor having means, connected thereto, for inductively driving therotor through the wall 0f said housing.

4. The device as recited in claim 1 wherein the means for reducing thepressure at the outlet of said turbomolecular pump includes a getter ionpump and a cryogenie pump.

5. The device as recited in claim 4 wherein said turbomolecular pump hasa rotor having means, connected thereto, for inductively driving therotor through the wall of said housing.

6. The device as recited in claim 1 wherein said turbomolecular pump hasa rotor having means, connected thereto, for inductively driving therotor through the wall of said housing.

4 7. The device as recited in claim 6 wherein the turbomolecular pumprotor is supported by magnetic bearings.

References Cited UNITED STATES PATENTS 3,066,849 12/1962 Beams.

3,137,551 6/1964 Mark 62-55.5 XR 3,189,264 6/1965 Becker 230-118 X3,226,012 12/1965 Trask 230-118 X 3,399,827 9/1968 Schwartzman 230-118 X3,443,390 5/1969 Webb 62-55.5 3,485,054 12/1969 Hogan G12-55.5

r MARK M. NEWMAN, Primary Examiner 0 W. I. KRAUSS, Assistant ExaminerU.S. Cl. X.R.

